Previous reports from a variety of sources have strongly suggested that the prophylactic administration of platelets to thrombocytopenic patients with acute leukemia significantly enhances their chance for a remission and averts hemorrhagic complications. These data were mostly based on observations made among leukemic patients previously unexposed to platelet transfusions during their first course of induction therapy. Yet, they have been translated into a requirement for continued prophylactic transfusion of thrombocytopenic leukemic patients even after they have developed platelet antibodies. This practice constitutes a large usage of platelets in the United States even though its long range effects are not only untested, but may be deleterious. This usage of platelet transfusions will be studied in a randomized manner. One of the major complications of transfusion of human blood products is the development of viral hepatitis. The incidence is believed to be high among patients receiving platelet transfusions because of the large number of human exposures. While the mortality rate directly attributable to icteric hepatitis is relatively low among transfused leukemic patients, they constitute a hazard to their families and the development of anicteric hepatitis may limit the administration of chemotherapy, prolong the period of pancytopenia and decrease the chances of obtaining a remission. The majoriy of hepatitis acquired by transfusion today is non-A non-B hepatitis which may be prevented by the prophylactic administration of immune human serum gamma globulin. This will be tested among patients of this study receiving platelet transfusions to ascertain if it decreases the occurence of liver function abnormalities, the period of pancytopenia secondary to chemotherapy and increases the rate of remission. Serial serum and fecal specimens will be obtained from patients of this study and stored for use for the possible development of antigen-antibody test systems for the immunological identification of non-A non-B post-transfusion hepatitis viruses.